Hitherto, the television signals used in producing cinemas are video data of 24-frame rate (i.e., 24 frames/sec). A standard television signal, such as an NTSC television signal, is composed of 30-frame rate video data. To broadcast a cinema video program by television, a telecine device is used to convert images recorded on film into video signals. In the telecine device, an imaging element captures the images on the film, at the 24-frame rate, generating a 24-frame rate video signal. The 24-frame rate video signal is subjected to 2-3 pull-down process. A 30-frame video signal (an NTSC television signal) is thereby generated. The 2-3 pull-down process is a process of converting two fields to three fields, for every four fields. For example, of the top and bottom fields that constitute a frame, the top field is repeated, thereby converting the two fields to three fields. The field added by performing the 2-3 pull-down process is called “repeated field.”
Off-line edition and on-line edition are performed on the 30-frame video signal generated by the 2-3 pull-down process, in order to provide a television program that is to be broadcast. The off-line edition is a process of determining an edition point for the video material of 30-frame rate, by the use of an editing system composed of inexpensive devices, and thereby preparing an edition list called “EDL (Edit Decision List).” The on-line edition is a process of generating a master television program from the edition list prepared by performing the off-line edition and the original video material of 30-frame rate.
The conventional editing system is designed to record, reproduce and transmit video signals of 30-frame rate. This is because the standard television signals, i.e., NTSC television signals, are of 30-frame rate. The VHS-format VTRs or the like, which have been widely used as off-line editing systems, can indeed record, reproduce and transmit the standard NTSC television signals of 30-frame rate, but cannot record, reproduce or transmit television signals of 24-frame rate.
Under these circumstances, it is recently demanded that the original video material be obtained by video cameras at the 24-frame rate, not at the 30-frame rate, thereby to provide original video material of 24-frame rate. This is because, in the digital television broadcasting (DTV broadcasting) recently started in some countries, the video data transmitted to households are encoded in accordance with the MPEG2 standards and distributed in the form of a transport stream. As described in the PCT application (WO 00/13418) filed by the assignee of this application, any 30-frame rate, video program prepared by the 2-3 pull-down process must be converted back to a 24-frame rate program by means of the inverse 2-3 pull-down process, before it is encoded in the MPEG2 format. The 30-frame rate program needs to be so converted, because the MPEG2 data-compressing algorithm utilizes bi-directional, predicting coding, wherein two pictures preceding and following the picture of interest, respectively, are used, in order to increase the data-compression rate. If a video signal, which contains a redundant field, e.g., a repeated field, will represent an image of extremely low poor quality if it is encoded without being modified.
Movie video programs and television programs are now converted, in increasing numbers, to data streams compressed by MPEG2 coding technique. The data streams thus generated are recorded on recording media such as DVD discs. More and more DVD discs, each with a video program recorded on it, are now sold.
In favor of DTV technique and DVD technique, it is increasingly demanded that video cameras take pictures at 24-frame rate, thereby to generate 24-frame rate, original video materials.
However, the off-line editing system composed of an inexpensive apparatus, such as the home-use VHS VTR, can record, reproduce and transmit only video signals of 30-frame rate. To accomplish an off-line editing process, 24-frame rate, video programs must be subjected to the 2-3 pull-down process, thereby to generate 30-frame rate, video programs.
If original source video data of 24-frame rate is converted to video data of 30-frame rate by the 2-3 pull-down process, however, the 24-frame rate time codes that correspond to the original source video data cannot be transmitted, though the 30-frame rate time codes that correspond to 30-frame rate video data can be transmitted. This is because only time codes of the video data to be transmitted are defined in the SMPTE-12M standards of transmitting time codes. According to the SMPTE-12M standards, the only timing codes of 30-frame rate can be superposed on carrier waves during the blanking period of, for example, a 30-frame rate video signal. During the blanking period of a 24-frame rate video signal, only time codes of 24-frame rate can be superposed on carrier waves.
In other words, 30-frame rate time code cannot be identified with the corresponding 24-frame rate time codes during the off-line editing process. It is therefore impossible to identify the frames of 30-frame rate video data with the corresponding 24-frame rate video data. Consequently, frames, each containing a repeated field, remain in the master video program. If this occurs, particularly if repeated fields remain in the master video program, the repeated fields will be removed when the MPEG2 coding is carried out. This may results in the problem that the video signals will have but insufficient fields.
Another problem arises. An edition list of 30-frame rate, if any prepared, cannot be used as an edition list in editing any original source video program of 24-frame rate.